Abstract

Human population studies show that dietary red and processed, but not white, meats are associated with increased risk of colorectal cancer but dietary fibre appears to be protective. We examined whether dietary cooked red or white meat had differential effects on colonic DNA damage in rats and if resistant starch (RS), a dietary fibre component, provided protection. Rats were fed diets containing approximately 15, 25 or 35% of cooked beef or chicken, both with or without 20% high-amylose maize starch (HAMS) as a source of RS, for 4 weeks. DNA single-strand breaks (SSB) and double-strand breaks (DSB) were measured in isolated colonocytes (by comet assay) along with apoptosis levels, colonic mucus thickness and large bowel short-chain fatty acids (SCFA). Both red and white meat increased colonocyte SSB and DSB dose dependently but damage was substantially greater with red meat. Dietary HAMS prevented these increases. Apoptotic cell numbers were increased dose dependently by red meat irrespective of HAMS feeding, whereas white meat only increased apoptotic cell numbers in the presence of HAMS. Red meat induced greater colonic mucus layer thinning than white meat but HAMS was protective in both cases. HAMS induced increases in large bowel SCFA, including butyrate, and significantly lowered concentrations of phenols and cresols. We have demonstrated that dietary red meat causes greater levels of colonic DNA SSB and DSB than white meat, consistent with the epidemiological data. Dietary RS protects against this damage and also against loss of the mucus barrier, probably through increased butyrate production.